Response to soil salinity of two chickpea varieties differing in drought tolerance

Two chickpea varieties, differing in drought tolerance, were grown in lysimeters filled with clay, and were irrigated with waters of three different salinity levels. Under non-saline conditions, both varieties, slightly differing in pre-dawn leaf water potential during the growth period, gave almost the same yield.Salinity had a slight effect on the leaf water potential and the osmotic adjustment. Both were slightly higher for the drought tolerant variety, but much lower in comparison with sugar beet, tomato and lentil. The drought tolerant variety showed an earlier senescence in leaf and dry matter development and flowering which were accelerated by salinity. The drought sensitive variety, however, showed under slightly saline conditions (EC_e=2.5 dS/m) from 135 days after sowing onwards a different behaviour by the growth of new leaves and flowers, a delay in senescence, leading to the same yield as under non-saline conditions. Under saline conditions (EC_e=3.8 dS/m) the drought sensitive variety showed the same yield reduction of about 70% as the drought tolerant variety.     

Short term effects of saline irrigation on evapotranspiration from lysimeter-grown citrus trees

Eight-year-old Murcott orange trees grown in greenhouse lysimeters filled with sandy soil were subjected to irrigation with saline water to investigate the influence of salinity on daily evapotranspiration (ET). The study was conducted in Japan from 1 August to 15 September 2000. The study duration was divided into three periods of about 2 weeks each. In period I, all lysimeters planted with a tree were irrigated with 60 mm of non-saline water at the water content of 70% of field capacity (FC). Salinity treatments for period II started on 14 August. The treatments during period II were as follows: Lysimeter 1 (L1) had 32 mm non-saline water with an electrical conductivity (EC_I) of 1.0 dS/m applied. At the same time Lysimeter 2 (L2) had 32 mm of saline water with an EC_I of 8.6 dS/m applied when the water content decreased to 70% of FC. Lysimeter 3 (L3) had 16 mm saline water (EC_I=8.6 dS/m) applied at 85% of FC. The irrigation amounts during period II were equal to those corresponding to 1.2 times of water required to reach FC. Treatments in period III were the same as in period I.Daily ET was similar for all weighing lysimeters during period I. The average relative ET for L2 and L3 with respect to L1 (L2/L1 and L3/L1) were similar during this period, with a mean value of 0.99. During period II, ET from L1 was consistently higher than that from L2 and L3. In addition, L3 with a higher irrigation frequency because of irrigation at higher soil water content resulted in higher ET than L2. The average relative ET of period II was 0.71 and 0.88 for both L2 and L3. During the last half of period III, reductions occurred in the ET differences between the saline treatments (L2 and L3) and non-saline control (L1).Evaporation rates from soil did not exceed 0.7 mm per day. Transpiration rates from L1, L2 and L3 during period II varied between 6.3 and 3.1 mm per day, 4.5 and 2.2 mm per day, and 5.8 and 3.0 mm per day, respectively. The results reflected a tangible difference of water extraction by roots from individual soil layers. Maximum water uptake by these trees was observed at layer of 30–60 cm. Nevertheless, no clear differences in water extraction pattern between trees were observed.Approximately, 95% of drainage occurred during the first 2 days following irrigation. The electrical conductivity of soil water (EC_S) and the electrical conductivity of drainage water (EC_D) for the saline water treatments (L2 and L3), compared to the control (L1) were significantly different during period II. EC_S values were 2–5 times higher in saline treatments compared to the control treatment. After irrigating trees with saline water, EC_S increased from 5 to 14 and 16 dS/m in L2 and L3, respectively. Similarly, in both saline treatments, EC_D values were greatly increased after irrigation. During period III, EC_D values increased from 5 to 8 dS/m in L2, and from 3 to 11 dS/m in L3. By contrast, EC_S declined from 14 to 5 dS/m in L2, and from 16 to 3 dS/m in L3 over the same period.     

Effect of initial soil salinity and subirrigation water salinity on potato tuber yield and size

A field lysimeter study was conducted to investigate the effect of initial soil salinity and salinity level of brackish subirrigation water on tuber weight and tuber size of three potato (Solanum tuberosum L.) cultivars (Kennebec, Norland and Russet Burbank) under simulated arid conditions. Both saline and non-saline initial soil conditions were simulated in a total of 36 lysimeters. Eighteen lysimeters were flushed with fresh water (0.2 dS/m), while the remaining 18 lysimeters were flushed with brackish water (2 dS/m). For each soil condition, two subirrigation water concentrations, 1 and 9 dS/m, were used in nine lysimeters each. For each subirrigation water treatment, three potato cultivars were grown. In all lysimeters, water table was maintained at 0.4 m from the soil surface. Arid conditions were simulated by covering the lysimeter top with plastic mulch, allowing the potato shoots to grow through a cut in the mulch. The average root zone salinities (EC_w) were found to be 1.2 and 1.5 dS/m in non-saline lysimeters subirrigated with 1 and 9 dS/m waters, respectively. The corresponding salinities were 3.2 and 3.7 dS/m in the saline lysimeters. Across cultivars, there was no significant effect of either initial soil salinity or subirrigation water salinity on total tuber weight. However, the weight of Grade A tubers was higher in non-saline soil than in saline soil. Kennebec and Russet Burbank Grade A tuber weights were not affected by the initial soil salinity. On the contrary, a significant reduction in Grade A and total tuber weight under initially saline soil was evident for the Norland cultivar.     

Response of safflower (Carthamus tinctorius L.) to saline soils and irrigation: I. Consumptive water use

Salt-tolerant crops can be grown with saline water from tile drains and shallow wells as a practical strategy to manage salts and sustain agricultural production in the San Joaquin Valley (SJV) of California. Safflower (Carthamus tinctorius L.) was grown in previously salinized plots that varied in average electrical conductivity (EC_e) from 1.8 to 7.2 dS m⁻¹ (0–2.7 m depth) and irrigated with either high quality (EC_i<1 dS m⁻¹) or saline (EC_i=6.7 dS m⁻¹) water. One response of safflower to increasing root zone salinity was decreased water use and root growth. Plants in less saline plots recovered more water on average (515 mm) and at a greater depth than in more salinized plots (435 mm). With greater effective salinity, drainage increased with equivalent water application rates. Seed yield was not correlated with consumptive water use over the range of 400–580 mm. Total biomass and plant height at harvest were proportional to water use over the same range. Safflower tolerated greater levels of salinity than previously reported. Low temperatures and higher than average relative humidity in spring likely moderated the water use of safflower grown under saline conditions.     

Salt tolerance analysis of chickpea,faba bean and durum wheat varieties: I. Chickpea and faba bean

Two varieties of chickpea (Cicer arietinum L.) and faba bean (Vicia faba), differing in drought tolerance according to the classification of the International Center for Agronomic Research in Dry Areas (ICARDA), were irrigated with waters of three different salinity levels in a lysimeter experiment to analyse their salt tolerance.The drought-sensitive varieties are more salt tolerant than the drought-tolerant varieties. Under saline conditions, the drought-sensitive varieties show a much higher yield up to a salinity threshold, corresponding with an electrical conductivity (EC_e) between 2.5 and 3 dS/m for chickpea and between 5.5 and 6 dS/m for faba bean.The drought-sensitive varieties are able to improve or maintain the water-use efficiency when irrigated with saline water. This ability can be ascribed to

• •the larger biomass production owing to the later senescence, which allows a better utilization of the irrigation water;
• •the late flowering of chickpea.

     

Irrigation management and hydrosalinity balance in a semi-arid area of the middle Ebro river basin (Spain)

The analysis of irrigation and drainage management and their effects on the loading of salts is important for the control of on-site and off-site salinity effects of irrigated agriculture in semi-arid areas. We evaluated the irrigation management and performed the hydrosalinity balance in the D-XI hydrological basin of the Monegros II system (Aragón, Spain) by measuring or estimating the volume, salt concentration and salt mass in the water inputs (irrigation, precipitation and Canal seepage) and outputs (evapotranspiration and drainage) during the period June 1997–September 1998. This area is irrigated by solid-set sprinklers and center pivots, and corn and alfalfa account for 90% of the 470 ha irrigated land. The soils are low in salts (only 10% of the irrigated land is salt-affected), but shallow (<2 m) and impervious lutites high in salts (average EC_e=10.8 dS m⁻¹) and sodium (average SAR_e=20 (meq l⁻¹)^0.5) are present in about 30% of the study area.The global irrigation efficiency was high (Seasonal Irrigation Performance Index=92%), although the precipitation events were not sufficiently incorporated in the scheduling of irrigation and the low irrigation efficiencies (60%) obtained at the beginning of the irrigated season could be improved by minimising the large post-planting irrigation depths given to corn to promote its emergence. The salinity of the irrigation water was low (EC=0.36 dS m⁻¹), but the drainage waters were saline (EC=7.5 dS m⁻¹) and sodic (SAR=10.3 (meq l⁻¹)^0.5) (average values for the 1998 hydrological year) due to the dissolution and transport of the salts present in the lutites. The discharge salt loading was linearly correlated (P<0.001) with the volume of drainage. The slope of the daily mass of salts in the drainage waters versus the daily volume of drainage increased at a rate 25% higher in 1997 (7.6 kg m⁻³) than in 1998 (6.1 kg m⁻³) due to the higher precipitation in 1997 and the subsequent rising of the saline watertables in equilibrium with the saline lutites. Drainage volumes depended (P<0.001) on irrigation volumes and were very low (194 mm for the 1998 hydrological year), whereas the salt loading was moderate (13.5 Mg ha⁻¹ for the 1998 hydrological year) taking into account the vast amount of salts stored within the lutites. We concluded that the efficient irrigation and the low salinity of the irrigation water in the study area allowed for a reasonable control of the salt loading conveyed by the irrigation return flows without compromising the salinization of the soil’s root-zone.     

Simulations on direct and cyclic use of saline waters for sustaining cotton–wheat in a semi-arid area of north-west India

A validated agro-hydrological model soil water atmosphere plant (SWAP) was applied to formulate guidelines for irrigation planning in cotton–wheat crop rotation using saline ground water as such and in alternation with canal water for sustainable crop production. Six ground water qualities (4, 6, 8, 10, 12 and 14 dS/m), four irrigation schedules with different irrigation depths (4, 6, 8 and 10  cm) and two soil types (sandy loam and loamy sand) were considered for each simulation. The impact of the each irrigation scenario on crop performance, and salinization/desalinisation processes occurring in the soil profile (0–2 m) was evaluated through Water Management Response Indicators (WMRIs). The criterion adopted for sustainable crop production was a minimum of pre-specified values of ET_rel (≥0.75 and ≥0.65 for wheat and cotton, respectively) at the end of the 5th year of simulation corresponding to minimum deep percolation loss of applied water. The extended simulation study revealed that it was possible to use the saline water upto 14 dS/m alternatively with canal water for cotton–wheat rotation in both sandy loam and loamy sand soils. In all situations pre-sown irrigation must be accomplished with canal water (0.3–0.4 dS/m). Also when the quality of ground water deteriorates beyond 10 dS/m, it was suggested to use groundwater for post-sown irrigations alternately with canal water. Generally, percolation losses increased with the increase in level of salinity of ground water to account for leaching and thus maintain a favourable salt balance in the root zone to achieve pre-specified values of ET_rel.     

Groundwater quality in CR-V irrigation district (Bardenas I,Spain): Alternative scenarios to reduce off-site salt and nitrate contamination

Irrigated agriculture may negatively affect groundwater quality and increase off-site salt and nitrate contamination. Management alternatives aimed at reducing these potential problems were analysed in the 15498 ha CR-V Irrigation District (Spain) by monitoring 49 wells and modelling the hydrological regime in a representative well of the Miralbueno Aquifer. Groundwaters presented low to moderate electrical conductivity (EC) (mean = 0.89 dS/m) and high [NO₃⁻] (mean = 94 mg/L). The groundwater depth (GWD) during the 2001 hydrological year responded to the annual cycles of precipitation and irrigation as well as to the secondary cycles derived from irrigation scheduling. GWD were consistently simulated by the groundwater BAS-A model. Model results indicate that an increase in irrigation efficiency and the pumping of groundwater for irrigation will decrease GWD and aquifer's discharge by 56–70%, depending on scenarios. These recommendations will save good-quality water in the reservoir, will be beneficially economical to farmers, and will minimize off-site salt and nitrogen contamination.     

Potential nitrate losses under different agricultural practices in the pampas region,Argentina

Fertilization is an important cause of groundwater contamination with nitrate in agricultural soils. The objectives of the present work were: (i) to quantify the nitrate leaching in two fertilized and irrigated soils of the Pampas Region, Argentina; (ii) to test the ability of the NLEAP model to predict residual and leached nitrate in those soils. The soils were a Typic Hapludoll and a Typic Argiudoll. The treatments were: natural grassland never ploughed or fertilized; maize with a short history of fertilization; maize with a long history of fertilization; irrigated maize with a long history of fertilization. Both sites were sampled after harvest in two consecutive years to a 3 m depth. Residual nitrate and potential losses below 150 cm were estimated by NLEAP model. The average amount of nitrate (NO₃-N), including values of all treatments, in the upper layer (0–1.5 m) was 128 kg NO₃-N ha⁻¹ in the first sampling date and was consistently lower in the second sampling date (38 kg NO₃-N ha⁻¹). In the deeper layer (1.5–3 m) these values were 80 and 28 kg NO₃-N ha⁻¹ for the first and second sampling date, respectively. Differences between the non-fertilized and the fertilized treatments were significantly smaller in the second sampling date. Obtained results suggest that the rainfall previous to the first sampling was not enough to displace nitrate below 3 m depth. The afterwards heavy rainfall leached nitrate previously accumulated in the soil. Complementary irrigation did not affect nitrate movements. Simulated residual and leached nitrate showed a high correlation with observed values. Nitrate leaching was more associated to rainfall regime and crop yields than to soil type. Simulated residual and leached nitrate showed a high correlation with measured values in both soils, which suggests that NLEAP was appropriate to predict soil nitrate leaching under the studied conditions.     

Yield and foliar injury responses of mature plum trees to salinity

Summary The salt tolerance of mature Santa Rosa plum trees was assessed on 20-year-old trees grown in the San Joaquin Valley of California. The experimental design consisted of six levels of irrigation water salinity (electrical conductivities of 0.3 to 8 dS/m) replicated five times with each replication consisting of ten trees. Salinity treatments imposed in March 1984 did not influence tree yields harvested in June 1984. In 1985, the second year of treatments, yield from the highest salt treatment (electrical conductivity of irrigation water, EC _i , of 8 dS/m) was reduced by half; the number of fruit harvested was reduced 40%, and fruit size was reduced significantly. Foliar damage was so severe by the end of 1985 that nonsaline water was applied to the two highest salt treatments (EC _i = 6 and 8 dS/m) in an attempt to restore tree vigor. In 1986 salt effects had become progressively worse on the continuing saline treatments. A linear piece-wise salt tolerance curve is presented for soil salinity values, expressed as the electrical conductivity of saturated extracts (EC _e ) integrated to a soil depth of 1.2 m over a 2-year period. The salt tolerance threshold for relative yield (Y _r ) based on 3 years of data was 2.6 dS/m and yield reduction at salinity levels beyond the threshold was 31% per dS/m (Y _ir=100 – 31 [EC _e – 2.6]j). Significant foliar damage occurred when leaf chloride concentrations surpassed 200 mmol/kg of leaf dry weight (0.7%). Sodium concentrations in the leaves remained below 10 mmol/kg (0.02%) until foliar damage became severe. This suggests that chloride was the dominant ion causing foliar damage.     

Reduction in growth and yield of Jerusalem artichoke caused by soil salinity

Summary The salt tolerance of irrigated Jerusalem artichokes (Helianthus tuberosus L.) was assessed in terms of biomass of both above ground parts and tubers in greenhouse and field trials. Salinity of irrigation water ranged from 0.7 to 12 dS m^–1 in the greenhouse trial and from 0.2 to 10 dS m^–1 in the field trial. Yield response of the dry matter of tubers of greenhouse-grown plants and of above ground parts of greenhouse-grown and fieldgrown plants, fell within the moderately tolerant category of Maas and Hoffman (1977). However, tuber yields in the field on a heavy clay loam fell within the moderately sensitive category, described by the equation, Y = 100 – 9.62 (ECe-0.4), where Y = yield (t ha^–1) as a % of that under non-saline conditions and EC_e = electrical conductivity of saturation extract in the rootzone (0–30 cm). The Cl concentration of leaves increased linearly with increasing external salinity and increased from tubers to stems to leaves. In contrast, leaf Na remained low except at the highest salinities, despite consistently higher stem Na; indicating some mechanism for restriction of leaf Na up to a certain external salinity.     

Trickle and sprinkler irrigation of potato (Solanum tuberosum L.) in the Middle Anatolian Region in Turkey

The potato (Solanum tuberosum L.) is widely planted in the Middle Anatolian Region, especially in the Nigde-Nevsehir district where 25% of the total potato growing area is located and produces 44% of the total yield. In recent years, the farmers in the Nigde-Nevsehir district have been applying high amounts of nitrogen (N) fertilizers (sometimes more than 900 kg N ha⁻¹) and frequent irrigation at high rates in order to get a much higher yield. This situation results in increased irrigation and fertilization costs as well as polluted ground water resources and soil. Thus, it is critical to know the water and nitrogen requirements of the crop, as well as how to improve irrigation efficiency. Field experiments were conducted in the Nigde-Nevsehir (arid) region on a Fluvents (Entisols) soil to determine water and nitrogen requirements of potato crops under sprinkler and trickle irrigation methods. Irrigation treatments were based on Class A pan evaporation and nitrogen levels were formed with different nitrogen concentrations.The highest yield, averaging 47,505 kg ha⁻¹, was measured in sprinkler-irrigated plots at the 60 g m⁻³ nitrogen concentration level in the irrigation treatment with limited irrigation (480 mm). Statistically higher tuber yields were obtained at the 45 and 60 g m⁻³ nitrogen concentration levels in irrigation treatments with full and limited irrigation. Maximum yields were obtained with about 17% less water in the sprinkler method as compared to the trickle method (not statistically significant). On the loam and sandy loam soils, tuber yields were reduced by deficit irrigation corresponding to 70% and 74% of evapotranspiration in sprinkler and trickle irrigations, respectively. Water use of the potato crop ranged from 490 to 760 mm for sprinkler-irrigated plots and 565–830 mm for trickle-irrigated treatments. The highest water use efficiency (WUE) levels of 7.37 and 4.79 kg m⁻³ were obtained in sprinkle and trickle irrigated plots, respectively. There were inverse effects of irrigation and nitrogen levels on the WUE of the potato crops. Significant linear relationships were found between tuber yield and water use for both irrigation methods. Yield response factors were calculated at 1.05 for sprinkler methods and 0.68 for trickle methods. There were statistically significant linear and polynomial relationships between tuber yield and nitrogen amounts used in trickle and sprinkler-irrigated treatments, respectively. In sprinkler-irrigated treatments, the maximum tuber yield was obtained with 199 kg N ha⁻¹. The tuber cumulative nitrogen use efficiency (NUE_cu) and incremental nitrogen use efficiency (NUE_in) were affected quite differently by water, nitrogen levels and years. NUE_cu varied from 16 to 472 g kg⁻¹ and NUE_in varied from 75 to 1035 g kg⁻¹ depending on the irrigation method. In both years, the NH₄-N concentrations were lower than NO₃-N, and thus the removed nitrogen and nitrogen losses were found to be 19–87 kg ha⁻¹ for sprinkler methods and 25–89 kg ha⁻¹ for trickle methods. Nitrogen losses in sprinkler methods reached 76%, which were higher than losses in trickle methods.     

Spatial variability of solutes in a pecan orchard surface-irrigated with untreated effluents in the upper Rio Grande River basin

Untreated effluents are blended with water from the Rio Grande River and used for irrigation in the Juarez Valley of northern Mexico. Effluents are a source of nutrients, but may also be a source of heavy metal contamination. This study was conducted to characterize deposition patterns of selected metals, salts, and total nitrogen in a 6 ha pecan (Carya illinoenisis K.) orchard which had healthy-to-stunted trees with dieback. Orchard soil was collected along multiple transects to depths of 1.2 m, with spacing every 20 m. All solutes showed a magnitude variability in particular ions. Chromium, Ni, Pb, and Cd concentrations averaged <14 mg kg⁻¹. Soil Na, Ca, K, Mg, SO₄, Cl and NO₃–N averaged <100 mg kg⁻¹. Total N was <0.21%. Most solutes accumulated at the soil surface with the exception of Na and SO₄. Linear semi-variograms best described spatial metal deposition and surface clay content with a range of influence >189 m. Spherical semi-variograms best described spatial distribution of salts and total N, but accounted <50% of the variability. The solubility of solutes in moderately alkaline irrigation water and their specific behavior in calcareous soils likely affected deposition patterns. Estimated metal loads from irrigation over a 15-year period were <3 kg ha⁻¹, but about 187 Mg ha⁻¹ for total dissolved solids (salts). Pecan leaf tissue showed no signs of heavy metal accumulation. Suboptimum pecan growth was associated with salt accumulation in a clayey area with low permeability. Salts, in particular Na, rather than metals may be the most important inorganic contaminants for irrigated agriculture in this region. Salt loads in irrigation waters are expected to increase as agriculture increasingly relies on urban effluents too expensive to convert to potable water.     

Rice growth and yield respond to changes in water depth and salinity stress

Depth of standing water in rice paddy fields is an important agronomic parameter in the management of irrigation-related salinity problems. It was hypothesized that reductions in the yield of rice under salinity stress can be ameliorated by adjusting the water depth. This study was designed to determine the interactive effects of salinity and water depth on seedling establishment and grain yield in rice. Plants were grown in a greenhouse and irrigated with nutrient solutions amended with NaCl and CaCl₂ (5:1 molar concentrations). Treatments were three salt levels with electrical conductivities at 0.9, 3.3 and 6.0 dS m⁻¹ and six water depths at 4, 7, 10, 13, 16 and 20 cm. The effects of both salinity and water depth were significant on plant growth and yield. However, there was no interaction between the effects of salinity and water depth. Reductions in seedling establishment and grain yield with increases of salinity and water depth resulted from a simple combination of the two different stresses on plants. Highly significant negative correlations were identified between water depth and seedling establishment and also between water depth and grain yield when data were combined across salt levels. Generally, plants performed better with respect to seedling establishment and grain yield in shallow water (i.e. <10 cm) than in deep water (i.e. >10 cm). Under salt stress, the effect of water depth was significant for panicle number, but not significant for panicle weight. The loss of grain yield under salt stress with the increases of water depth was mainly due to reduction in fertile tiller number. We suggest that water depth be lowered during the initiation and growth of productive tillers. However, the practice by lowering water depth must be incorporated with appropriate field management such as the increase of irrigation frequency, precision leveling, and effective weed control methods.     

Shoot growth and fruit development of muskmelon under saline and non-saline soil water deficit

In irrigated agriculture, the production of biomass and marketable yield depend largely on the quantity and salinity of the irrigation water. The sensitivity of field-grown muskmelon (Cucumis melo L. cv. Galia) to water deficit was compared, using non-saline (EC_i= 1.2 dS m^–1) and saline (EC_i=6.3 dS m^–1) water. Drip irrigation was applied at 2-day intervals at seven different water application rates for each water quality, including a late water-stress treatment. Neutron scattering measurements showed that the soil layers below the root zone remained dry throughout the experiment, indicating negligible deep percolation. Thus, the sum of the seasonal amount of applied water and the change in soil moisture approximated the cumulative evapotranspiration (ET). Gradual buildup of water and salt stresses resulted in small treatment effects on the size of the vegetative cover and large effects on leaf deterioration and fruit production. Crop responses to salinity may result from an osmotic component of the soil water potential or from other salt effects on the crop physiology. Relating plant data to cumulative ET allowed a distinction to be made between the effect on water availability and specific salinity effects. The relation between fruit fresh weight and ET was not sensitive to EC_i. The slopes for fruit dry weights were also insensitive to EC_i but the intercept was larger for saline treatments. At any given ET saline water increased fruit number, increased fruit dry matter content and decreased fruit netting, in comparison with non-saline water. The combination of salinity and soil-water deficit was detrimental to fruit quality. Saline soil-water deficit decreased the percentage of marketable (netted) fruit and caused an early end to the period of marketable fruit production. Non-saline soil-water deficit increased the percentage of marketable fruit and had no effect on the duration of the production period. Late non-saline water stress caused a pronounced increase in the percentage of marketable fruit.     

The effects of different irrigation regimes on cucumber (Cucumbis sativus L.) yield and yield characteristics under open field conditions

A study was conducted to determine the effects of different drip irrigation regimes on yield and yield components of cucumber (Cucumbis sativus L.) and to determine a threshold value for crop water stress index (CWSI) based on irrigation programming. Four different irrigation treatments as 50 (T-50), 75 (T-75), 100 (T-100) and 125% (T-125) of irrigation water applied/cumulative pan evaporation (IW/CPE) ratio with 3-day-period were studied.Seasonal crop evapotranspiration (ET_c) values were 633, 740, 815 and 903 mm in the 1st year and were 679, 777, 875 and 990 mm in the 2nd year for T-50, T-75, T-100 and T-125, respectively. Seasonal irrigation water amounts were 542, 677, 813 and 949 mm in 2002 and 576, 725, 875 and 1025 mm in 2003, respectively. Maximum marketable fruit yield was from T-100 treatment with 76.65 t ha⁻¹ in 2002 and 68.13 t ha⁻¹ in 2003. Fruit yield was reduced significantly, as irrigation rate was decreased. The water use efficiency (WUE) ranged from 7.37 to 9.40 kg m⁻³ and 6.32 to 7.79 kg m⁻³ in 2002 and 2003, respectively, while irrigation water use efficiencies (IWUE) were between 7.02 and 9.93 kg m⁻³ in 2002 and between 6.11 and 8.82 kg m⁻³ in 2003.When the irrigation rate was decreased, crop transpiration rate decreased as well resulting in increased crop canopy temperatures and CWSI values and resulted in reduced yield. The results indicated that a seasonal mean CWSI value of 0.20 would result in decreased yield. Therefore, a CWSI = 0.20 could be taken as a threshold value to start irrigation for cucumber grown in open field under semi-arid conditions.Results of this study demonstrate that 1.00 IW/CPE water applications by a drip system in a 3-day irrigation frequency would be optimal for growth in semiarid regions.     

Water use and lint yield response of drip irrigated cotton to the length of irrigation season

A 2-year experiment was conducted at Tal Amara Research Station in the Bekaa Valley of Lebanon to determine water use and lint yield response to the length of irrigation season of drip irrigated cotton (Gossypium hirsutum L.). Crop evapotranspiration (ET_crop) and reference evapotranspiration (ET_rye-grass) were directly measured at weekly basis during the 2001 growing period using crop and rye-grass drainage lysimeters. Crop coefficients (K_c) in the different growth stages were calculated as ET_crop/ET_rye-grass. Then, the calculated K_c values were used in the 2002 growing period to estimate evapotranspiration of cotton using the FAO method by multiplying the calculated K_c values by ET_rye-grass measured in 2002. The length of irrigation season was determined by terminating irrigation permanently at first open boll (S1), at early boll loading (S2), and at mid boll loading (S3). The three treatments were compared to a well-watered control (C) throughout the growing period. Lint yield was defined as a function of components including plant height at harvest, number of bolls per plant, and percentage of opened bolls per plant.Lysimeter-measured crop evapotranspiration (ET_crop) totaled 642 mm in 2001 for a total growing period of 134 days, while when estimated with the FAO method in 2002 it averaged 669 mm for a total growing period of 141 days from sowing to mature bolls. Average K_c values varied from 0.58 at initial growth stages (sowing to squaring), to 1.10 at mid growth stages (first bloom to first open boll), and 0.83 at late growth stages (early boll loading to mature bolls).Results showed that cotton lint yields were reduced as irrigation amounts increased. Average across years, the S1 treatment produced the highest yield of 639 kg ha⁻¹ from total irrigations of 549 mm, compared to the S2 and S3 treatments, which yielded 577 and 547 kg ha⁻¹ from total irrigations of 633 and 692 mm, respectively, while the control resulted in 457 kg ha⁻¹ of lint yield from 738 mm of irrigation water. Water use efficiency (WUE) was found to be higher in S1 treatment and averaged 1.3 kg ha⁻¹ mm⁻¹, followed by S2 (1.1 kg ha⁻¹ mm⁻¹), and S3 (1.0 kg ha⁻¹ mm⁻¹), while in the control WUE was 0.80 kg ha⁻¹ mm⁻¹. Lint yield was negatively correlated with plant height and the number of bolls per plant and positively correlated with the percentage of opened bolls. This study suggests that terminating irrigation at first open boll stage has been found to provide the highest cotton yield with maximum WUE under the semi-arid conditions of the Bekaa Valley of Lebanon.     

Soil salinity reduction and prediction of salt dynamics in the coastal ricelands of Bangladesh

Field experiments were conducted in moderately saline and saline soils during the 1996 dry and wet seasons and the 1997 dry season to document salt dynamics and establish their relationship with local hydrology. Topsoil (0–15 cm) salinity in the dry season varied from 4.0 to 9.0 dS m⁻¹ in moderately saline soils at Mirzapur and from 5.0 to 12.0 dS m⁻¹ in saline soils at Barodanga. In wet season, the corresponding figures were from 1.5 to 2.5 dS m⁻¹ and from 2.0 to 3.0 dS m⁻¹, respectively. Dry season cropping significantly reduced topsoil salinity at both the research sites. Overall peak salinity in non-plowed cropped lands was 25–38% lower than that of fallow lands, and in plowed cropped lands it was about 30–40% less than the non-plowed cropped lands.Multiple linear and non-linear regression models were developed to predict topsoil salinity of the fallow land for both moderately saline and saline soils by using daily rainfall and evaporation as independent variables. The prediction level was not significantly improved when a non-linear model was employed in place of linear model. Therefore, a linear model may be used to predict topsoil salinity of the coastal ricelands of Bangladesh.     

Opening floodgates in coastal floodplain drains: effects on tidal forcing and lateral transport of solutes in adjacent groundwater

The effects of opening tidal barriers (floodgates) upon water table levels and lateral transport of solutes adjacent drains was investigated at two sites on a coastal floodplain. The sites had contrasting geomorphology, soil texture and sediment hydraulic properties. The site with lower hydraulic conductivity (0.3–0.9 m day⁻¹) soils (Romiaka) also had a higher elevation and hydraulic gradients towards the drain. While floodgate opening at Romiaka enhanced the amplitude of pre-existing tidal interaction with adjacent shallow groundwater, altered hydraulic gradients and caused some salt seepage, lateral solute movement from the drain was highly attenuated (<10 m). The site with very high hydraulic conductivity soils (Shark Creek; >125 m day⁻¹) had a lower elevation and seasonally fluctuating hydraulic gradients. The introduction of a tidal pressure signal into the drain by opening the floodgate at Shark Creek caused tidal forcing of groundwater over 300 m from the drain. Floodgate opening at this site also caused changes in groundwater hydraulic gradients, leading to incursion of saline drain water into shallow groundwater over 80 m from the drain. Lateral movement of solutes was relatively rapid, due to macropore flow in oxidised acid sulfate soil horizons, and caused substantial changes to shallow groundwater chemical composition. Conversely, when groundwater hydraulic gradients were towards the drain at this site there was substantial lateral outflow of acid groundwater into drains. This study highlights the importance of assessing the hydraulic properties of soils next to drains on coastal floodplains prior to opening floodgates, particularly in acid sulfate soil backswamps, in order to prevent unintended saline intrusion into shallow groundwater.     

Irrigation with saline water in the reclaimed marsh soils of south-west Spain: impact on soil properties and cotton and sugar beet crops

The drained and irrigated marshes in south-west Spain are formed on soils of alluvial origin from the ancient Guadalquivir river estuary. The most important characteristics of these soils are the high clay content (about 70%), high salinity, and a shallow, extremely saline, water table. The reclaimed area near Lebrija, called Sector B-XII (about 15,000 ha), has been under cultivation since 1978. Some years, however, water supply for irrigation is limited due to drought periods. The objective of this work was to evaluate the effects of irrigation with high and moderately saline waters on soil properties and growth and yield of cotton and sugar beet crops. The experiments were carried out during 1997 and 1998 in a farm plot of 12.5 ha (250 m×500 m) in which a drainage system had been installed, consisting of cylindrical ceramic sections (0.3 m long) forming pipes 250 m long, buried at a depth of 1 m and spaced at intervals of 10 m. These drains discharge into a collecting channel perpendicular to the drains. Two subplots of 0.5 ha (20 m×250 m) each were selected. In 1997 cotton was growing in both subplots, and irrigation was applied by furrows. One subplot (A) was irrigated with fresh water (0.9 dS m⁻¹) during the whole season, while in the other subplot (B) one of the irrigations (at flowering stage) was with water of high salinity (22.7 dS m⁻¹). During 1998 both subplots were cropped with sugar beet. Subplot A was irrigated with fresh water (1.7 dS m⁻¹) during the whole season, while in subplot B two of the irrigations were with moderately saline water (5.9–7.0 dS m⁻¹). Several measurement sites were established in each subplot. Water content profile, tensiometric profile, water table level, drainage water flow, soil salinity, and crop development and yield were monitored. The results showed that after the irrigation with high saline water (subplot B) in 1997 (cotton), the soil salinity increased. This increase was more noticeable in the top layer (0–0.3 m depth). In contrast, for the same dates, the soil of subplot A showed no changes. After five irrigations with fresh water, the salinity of the soil in the subplot B reached values similar to those before the application of saline water. In 1998 (sugar beet) the application of moderately saline water in subplot B also increased soil salinity, but this increase was lower than in 1997. The irrigation with high saline water affected crop development. Cotton growth was reduced in comparison with that in the subplot irrigated only with fresh water. Despite this negative effect on crop development, the crop yield was the same as in the subplot A. Sugar beet development did not show differences between subplots, but yield was higher in subplot B than in subplot A.